There is a fundamental gap in understanding how oxidative damage contributes to pathogenesis. Thus, the long-term goal is to elucidate how the release/clearance dynamics of several reactive oxygen species and small molecules in the brain underlie neurodegenerative disease states involving oxidative stress. Hydrogen peroxide (H2O2) is a reactive oxygen species that also serves as an important signaling molecule in normal brain function. Because H2O2 serves these distinct biological roles, H2O2 concentrations likely rise and fall in the extracellular space with precise spatial and temporal resolution, such that functional levels can be achieved for signaling while the pathological consequences resulting from unregulated generation are prevented. However, studies aimed at elucidating these dynamics have been hindered by the lack of a method for probing dynamic H2O2 fluctuations in living systems with molecular specificity. The goals of this research proposal are to enable the quantitative analysis of endogenous H2O2 fluctuations in real-time, and to elucidate how these molecular dynamics modulate those of dopamine (DA) in intact, functional brain tissue. H2O2 is implicated in the pathogenesis of Parkinson's disease. Simultaneous H2O2 and DA measurements will enable regulatory kinetics and mechanisms to be unraveled, investigation of the alteration of these mechanisms by disease or pharmacological agents, and clarification of the neurochemical processes that underlie motor dysfunction. Carbon-fiber microelectrodes will be employed with fast-scan cyclic voltammetry, as this approach provides a quantitative view of neurotransmission in discrete brain locations in real-time. The specific aims combine the development of new technology with innovative applications. They are: 1. To enable the precise characterization of H2O2 fluctuations in the extracellular space of specific brain nuclei, shedding light on its modulatory signaling role, extrasynaptic lifetime, sphere of influence, and diffusion profile under both normal and pathological conditions. These experiments will also demonstrate the extent to which various sources of H2O2 contribute to signaling within select brain nuclei. 2. To elucidate the precise physiological interaction between H2O2 and DA, and the role that these molecular dynamics play in the onset of motor complications associated with Parkinson's disease. In order to achieve these aims, powerful mathematical models will be developed and validated that can be used to interpret the effects of pharmacological agents on the balance between H2O2 generation and clearance. Existing analytical techniques will be modified to enable improved quantitative assessment in the face of chemical variability. The proposed research is significant because the results are expected to vertically advance and expand our understanding of the physiological roles played by H2O2 in the brain, and to shed light on whether oxidative stress is an initiator of dopaminergic dysfunction, or a consequence of that process. Ultimately, such knowledge will inform the development of improved therapeutic interventions, neuroprotective strategies, and promising antiparkinsonian drugs based on redox biology.